This invention relates to slurries of solid carbonaceous fuels in water. More particularly, it relates to such slurries which are pumpable and stable against sedimentation of the solid carbonaceous material.
There has been considerable interest recently in developing solid carbonaceous fuels such as coal and petroleum coke as a substitute for liquid hydrocarbon fuels. It has been proposed to use slurries of finely divided coke or coal suspended in fuel oil as a substitute for fuel oil. U.S. Pat. No. 4,082,516 is representative of a large body of prior art relating to fuel slurries comprised of solid carbonaceous material in liquid hydrocarbon fuel.
Similarly, there has been considerable activity in development of water-in-oil emulsions which are capable of carrying suspended solid fuel particles. U.S. Pat. No. 4,162,143 is representative of this approach.
Preparation of a solid fuel-water slurry suitable for use as a feed to a synthesis gas process is described in U.S. Pat. No. 4,104,035.
A solid fuel-water slurry having improved pumpability is described in U.S. Pat. No. 4,088,453.
Efforts to develop highly loaded, stable, pumpable coal slurries containing up to 70 percent by weight coal in water are described in an article by R. S. Schefflee entitled "Development and Evaluation of Highly Loaded Coal Slurries" published in May of 1978 in Proceedings of the First International Symposium on Coal-Oil Mixture Combustion, pp. 222-232. This article describes results of various carrier materials including Xanthan gum, modified corn starch, carboxymethyl cellulose and numerous related materials. An article by R. S. Shefflee and E. T. McHale entitled "Development and Evaluation of Highly Loaded Coal Slurries" published in November of 1979 in Proceedings of the Second International Symposium on Coal-Oil Mixture Combustion, pp. 1-6, also discusses results of a program to develop highly loaded coal-water slurry fuels. This article suggests that the best carrier is hydroxypropylated cornstarch.
Many existing marine boilers do not have the capability for recirculating or agitating fuel. This has resulted in a reluctance on the part of operators of such vessels to use solid fuel-water slurries, for fear of settling of solids from the slurries with resultant serious operating problems. Even though the prior art has reported some success in stabilizing solid fuel-water slurries by using various viscosity builders and gelling agents, there has been a continuing need for improved stabilization of such slurries.
It is accordingly an object of this invention to provide slurry fuels comprised of solid carbonaceous material in water which have a high stability against sedimentation of the solid material during storage.